THE RECORD OF THE ROCKS
WE do not know how life began upon the earth.
Biologists, that is to say, students of life, have made guesses about these beginnings, but we will not discuss them here. Let us only note that they all agree that life began where the tides of those swift days spread and receded over the steaming beaches of mud and sand.
The atmosphere was much denser then, usually great cloud masses obscured the sun, frequent storms darkened the heavens. The land of those days, upheaved by violent volcanic forces, was a barren land, without vegetation, without soil. The almost incessant rain-storms swept down upon it, and rivers and torrents carried great loads of sediment out to sea, to become muds that hardened later into slates and shales, and sands that became sand-stones. The geologists have studied the whole accumulation of these sediments as it remains to-day, from those of the earliest ages to the most recent. Of course the oldest deposits are the most distorted and changed and worn, and in them there is now no certain trace to be found of life at all. Probably the earliest
- Here in this history of life we are doing our best to give only known and established facts in the broadest way, and to reduce to a minimum the speculative element that must necessarily enter into our account. The reader who is curious upon this question of life's beginning will find a very good summary of current suggestions done by Professor L. L. Woodruff in President Lull's excellent compilation The Evolution of the Earth (Yale University Press). Professor H. F. Osborn's Origin and Evolution of Life is also a very vigorous and suggestive book upon this subject, but it demands a fair knowledge of physics and chemistry. Two very stimulating essays for the student are A. H. Church's Botanical Memoirs. No 183, Ox. Univ. Press.